Airflow control valve for use in an internal combustion engine

ABSTRACT

An airflow control valve is composed of a housing forming an air passage therein and an electromagnetically driven valve disposed in the air passage. The valve divides the air passage into an upstream passage having an air inlet port and a downstream passage having an outlet port open to an exhaust pipe. A barrier facing an exhaust gas blown back from the exhaust pipe is formed in the downstream passage in order to reduce an amount of deposits accumulating on and around the valve due to foreign particles contained in the exhaust gas. The barrier may be a dead end space in which the exhaust gas stagnates or a wall interfering with a flow of the exhaust gas. A one-way valve may be disposed immediately downstream of the valve to prevent the exhaust gas from flowing toward the valve.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority ofJapanese Patent Application No. 2004-240955 filed on Aug. 20, 2004, thecontent of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an airflow control valve for opening orclosing an air passage communicating with an exhaust gas passage in aninternal combustion engine, and more particularly to an airflow controlvalve for controlling an amount of secondary air supplied from an airpump to an exhaust pipe.

2. Description of Related Art

Examples of an airflow control valve for supplying secondary air to athree-way catalyzer in an exhaust pipe for raising temperature of thethree-way catalyzer when an engine is being started are disclosed inJP-A-2002-272080 and JP-A-2002-260919. The airflow control valvedisclosed therein includes an electromagnetic valve and a one-way valve.An essential portion of the airflow control valve is shown in FIG. 10attached hereto.

As shown in FIG. 10, the electromagnetic valve 102 contained in a valvehousing 104 is composed of a valve 106 for opening or closing an opening105 formed in the valve housing, a solenoid actuator for driving thevalve 106 in a direction to open the opening 105, and a coil spring 107for biasing the valve 106 in a direction to close the opening 105. Theone-way valve 103 is disposed at a boundary portion connecting the valvehousing 104 and an outlet casing 110. The one-way valve 103 is composedof a reed valve 112 for opening or closing an opening 111 formed in ametal plate 114 and a reed stopper 113 for protecting the reed valve112.

Air pressurized by an air pump (not shown) is introduced into the valvehousing 104, and the introduced air is supplied to a three-way catalyzer(not shown) in an exhaust pipe through an air passage shown with whitearrows when the valve 106 opens the opening 105. The one-way valve 103is opened by the air passing through the air passage and is closed byexhaust gas (shown with dotted arrows in FIG. 10) blown back from theexhaust pipe. The blown back exhaust gas that includes unburned gas,carbon particles and other small particles is prevented from enteringinto the valve housing 104 by the one-way valve 103.

In the conventional airflow control valve, however, following problemsare involved. When the valve 106 is closed, exhaust gas is blown backdue to pulsating pressure of the engine and enters into the outletcasing 110 as shown with dotted arrows in FIG. 10. Small particlescontained in the exhaust gas adhere to the reed valve 112, formingdeposits thereon. If the deposits are formed between the metal plate 114and the reed valve 112, the reed valve 112 becomes unable to close, andthe exhaust gas enters into valve housing 104 containing the valve 106therein. In other words, the reed valve 112 becomes unable to functionas the one-way valve for preventing the exhaust gas from being blownback into the valve housing 104. The deposits may be formed on the valve106 and the valve seat. If this happens, movement of the valve 106 ishindered, and the valve 106 may not be smoothly opened. As a result, thesecondary air cannot be sufficiently supplied to the three-waycatalyzer.

An exhaust gas control valve is conventionally used in an exhaust gasre-circulation system. In this system, part of the exhaust gas isintroduced into an air-intake pipe of an engine to reduce an amount ofnitrogen-oxides formulated in combustion by lowering a combustiontemperature. The re-circulating exhaust gas is supplied to the intakepipe through the exhaust gas control valve. The exhaust gas controlvalve is composed of a housing forming an exhaust gas passage therein, avalve for closing or opening the exhaust gas passage, and a coil springbiasing the valve in the closing direction. The valve is driven by amotor actuator in the opening direction.

Small particles contained in the exhaust gas adhere to the valve and thevalve seat in the exhaust gas control valve, forming deposits around thevalve. To reduce an amount of deposits accumulated around the valve, anexhaust gas recirculation valve having a side hole in the passage foraccumulating the deposits therein is proposed in JP-A-2002-339811.However, the small particles in the exhaust gas once entered into theside hole are highly possible to bounce out into the passage. Therefore,much effect cannot be expected for the proposed side hole.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedproblem, and an object of the present invention is to provide animproved airflow control valve, in which an amount of depositsaccumulating on a control valve and a one-way valve is reduced.

The airflow control valve has an air passage and an electromagneticallydriven valve disposed in the air passage. The air passage is dividedinto two passages by the valve, i.e., an upstream passage having aninlet port and a downstream passage having an outlet port. Secondary aircompressed by an air pump is introduced into the upstream passagethrough the inlet port and supplied from the downstream passage to anexhaust pipe of an internal combustion engine through the outlet port.An amount of air supplied to the exhaust pipe is controlled by openingor closing the valve. The outlet port is open to the exhaust pipe, andexhaust gas is blown back into the downstream passage.

A barrier facing the outlet port from which the exhaust gas enters intothe airflow control valve is disposed in the downstream passage toreduce an amount of the exhaust gas directly hitting the valve. Thus, anamount of deposits accumulating on and around the valve due to foreignparticles contained in the exhaust gas is reduced. The barrier may bemade in a form of a dead end space having a small opening facing theoutlet port. The exhaust gas entering into the airflow control valvestagnates in the dead end space, and some foreign particles are kepttherein. To prevent the foreign particles once kept in the dead endspace from bouncing out of the dead end space toward the valve, bentportions may be made at the opening of the dead end space. Aninterfering wall directly facing the outlet port may be made in thedownstream passage to form a stagnating space between the interferingwall and the outlet port.

Preferably, one-way valve for preventing the exhaust gas from enteringinto the upstream passage while permitting the secondary air to flowtherethrough is disposed immediately downstream of the valve. The valveis prevented from being directly hit by the exhaust gas blown back fromthe exhaust pipe. The one-way valve is also protected from beingdirectly hit by a large amount of the exhaust gas by the barrier, thedead end space or the interfering wall disposed in the downstreampassage.

The airflow control valve may be used as a valve for controlling anamount of exhaust gas to be re-circulated from an exhaust pipe into anintake pipe of an engine. In this case, the exhaust gas is introducedfrom the outlet port, and the inlet port is connected to the intake pipeof the engine.

According to the present invention, an amount of exhaust gas directlyhitting the valve and the one-way valve is reduced and an amount ofdeposits accumulating on and around the valve and the one-way valve isreduced. Accordingly, the airflow control valve can be operated withoutbeing hindered by accumulation of deposits. Other objects and featuresof the present invention will become more readily apparent from a betterunderstanding of the preferred embodiments described below withreference to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an airflow control valve as afirst embodiment of the present invention;

FIG. 2 is a cross-sectional view showing the same airflow control valveas shown in FIG. 1, including arrows showing flow directions of air andexhaust gas;

FIG. 3 is a cross-sectional view showing an airflow control valve as asecond embodiment of the present invention;

FIG. 4 is a cross-sectional view showing an airflow control valve as athird embodiment of the present invention;

FIG. 5 is a cross-sectional view showing an airflow control valve as afourth embodiment of the present invention;

FIG. 6 is a plan view showing an outlet casing used in the fourthembodiment shown in FIG. 5;

FIG. 7 is a cross-sectional view showing the same airflow control valveas shown in FIG. 5, including arrows showing flow directions of air andexhaust gas;

FIG. 8A is a plan view showing an outlet casing used in the airflowcontrol valve shown in FIG. 5, viewed from its topside;

FIG. 8B is a plan view showing a modified form of the outlet casingshown in FIG. 8A;

FIG. 9 is a plan view showing the same outlet casing as shown in FIG.8B, in an enlarged scale; and

FIG. 10 is a cross-sectional view showing a conventional airflow controlvalve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will be described withreference to FIGS. 1 and 2. In this embodiment, a stagnating space inwhich exhaust gas blown back from an exhaust pipe stagnates is providedin an outlet casing of an airflow control valve in order to reduceaccumulation of deposits on a control valve. The airflow control valveis disposed in an air passage for supplying secondary air to a three-waycatalyzer in an exhaust pipe. The secondary air is sent from amotor-driven air pump to the airflow control valve that includes anelectromagnetic valve for controlling an amount of the secondary airsupplied to the three-way catalyzer. Operation of the motor for drivingthe air pump and the electromagnetic valve is controlled by anelectronic control unit (ECU). The secondary air is supplied to thethree-way catalyzer to activate the catalyzer when an engine is beingstarted and an exhaust gas temperature is low.

As shown in FIG. 1, the airflow control valve is composed of a valvehousing 3 containing an electromagnetic valve 1 having a poppet-typevalve 2 therein, an outlet casing 9 having a one-way valve 6 and otherassociated components. An air passage (11, 12, 14, 16, 17) for supplyingthe secondary air to the three-way catalyzer is formed in the valvehousing 3 and the outlet casing 9.

The electromagnetic valve 1 includes the poppet-type valve 2, a solenoidactuator 4 for driving the valve 2 in the opening direction and a coilspring 5 for biasing the valve 2 in the closing direction. The valve 2is formed in a disc shape having a resilient rubber ring disposed aroundits outer periphery. The valve 2 is connected to a valve shaft 21 thatis reciprocated in the vertical direction. The valve 2 is seated on avalve seat 23 formed on a valve sheet frame 22 of the valve housing 3 toclose an opening 13. When the valve 2 is driven, the valve 2 is liftedfrom the valve seat 23 to open the opening 13. The valve shaft 21 isslidably inserted into a sleeve 25, and a seal rubber 24 is disposed toclose a small sliding gap between the sleeve 25 and the valve shaft 21to thereby prevent small particles from entering into the sliding gap.

The valve housing 3 is made of aluminum by die-casting, and includes ainner space for accommodating the solenoid actuator 4 and a connectingpipe 26 having an inlet port 10 for introducing the secondary airsupplied from the air pump. The outlet casing 9 is also made of aluminumby die-casting, and includes air passages 16, 17, an outlet port 18 tobe connected to the exhaust pipe and a dead end space 19 (describedlater in detail). An upper end of the outlet casing 9 is connected to aflange 39 formed at a lower end of the valve housing 3, and a one-wayvalve 6 is positioned at the upper end portion of the outlet casing 9. Acircular seal rubber 37 is disposed between the valve housing 3 and theoutlet casing 9 for hermetically seal the connecting portion. The airpassage formed in the valve housing 3 and the outlet casing 9 isseparated by the valve 2 into an upstream passage 11, 12 and adownstream passage 14, 16, 17.

The solenoid actuator 4 for driving the valve 2 is composed of asolenoid coil 28 wound around a coil bobbin 27, a pair of terminals 29for supplying electric power to the solenoid coil 28, a housing cover 30supporting the terminals 29, a cylindrical yoke 31, a cylindrical statorcore 32 connected to the yoke 31 forming a space for accommodating thesolenoid coil 28 therebetween, and a moving core 33 connected to thevalve shaft 21. The coil bobbin 27 is made of a resin material such aspolybutylene terephthalate (PBT) and fixedly positioned in a cylindricalspace between the yoke 31 and the stator core 32.

Upon supplying electric power to the solenoid coil 28 from the terminals29, the moving core 33 connected to the valve shaft 21 is drivendownward by magnetic field generated in the yoke 31 and the stator core32 thereby to open the valve 12 against the biasing force of the coilspring 5. The terminals 29 are connected to the ECU through a wireharness, and the operation of the electromagnetic valve 1 is controlledby the ECU.

At the bottom end of the stator core 32, a flange portion forming theair passage 12 is provided, and at a center portion of the stator core32, a thin wall portion 35 is formed to provide a high magneticresistance in the magnetic circuit. The moving core 33 moves downward toopen the valve 2 when the magnetic field is generated by the solenoidcoil 28. The valve shaft 21 is inserted into a center hole of the movingcore 33 and a center hole of a washer 36 so that a step formed on thevalve shaft 21 abuts the bottom end of the moving core 33, and the upperend of the valve shaft 21 is staked to fixedly connect the valve shaft21 to the moving core 33. The coil spring 5 is disposed outside of thesleeve 25, and its upper end is connected to the bottom of the movingcore 33 and its lower end is connected to a flange portion of the sleeve25, so that a biasing force of the coil spring 5 is given to the valve 2in the closing direction.

The one-way valve 6 is a valve for preventing the exhaust gas blown backfrom the exhaust pipe from entering into the valve housing 3 whileallowing the secondary air to flow therethrough. The one-way valve 6 iscomposed of a metal plate 41 that has plural openings 15, a reed valve 7for opening or closing the openings 15, and a reed valve stopper 8 forlimiting the reed valve 7 at its maximum open position. The metal plate41 is made of a metallic material such as aluminum and includes pluralopenings 15 formed in a mesh-like shape. The reed valve 7 is made of ametallic material such as a spring plate. One end of the reed valve 7 issupported on the metal plate 41 with screws 42 or the like, and theother end of the reed valve 7 is shaped in double tongues or tripletongues. On the surface of the mesh-like openings 15 of the metal plate41, a rubber seal is formed by baking. The reed stopper 8 is made of ametallic material. One end of the reed stopper 8 is connected to themetal plate 41, and the other end thereof is a free end having double ortriple tongues.

Now, the structure of the outlet casing 9 having the dead end space 19will be described in detail. The exhaust gas may be blown back from theexhaust pipe into the air passage 16, 17 through the outlet 18 due to apressure pulsation generated in the exhaust pipe. The exhaust gasincludes small particles consisting of unburned gas, carbon particles orthe like. These small particles accumulate on the reed valve 7 formingdeposits thereon. When the deposits are formed on the reed valve 7, thereed valve 7 may become impossible to close to prevent the exhaust gasfrom entering into the valve housing 3. To decrease the amount ofexhaust gas hitting the reed valve 7, barrier 51 is formed so that apassage surface 52 of the barrier 51 faces the outlet 18.

A dead end space 19 is formed inside of the barrier 51. One end of thedead end space 19 is an opening 54 facing the outlet 18, and the otherend thereof is closed with a hermetic plug 53. A center line of the headend space 19 is substantially directed to a center line of the outletport 18. The dead end space 19 is positioned in the downstream passage,i.e., downstream of the valve 2 and the one-way valve 6. The dead endspace 19 functions as a stagnating space in which the blown back exhaustgas stagnates, thereby reducing an amount of the exhaust gas directlyhitting the reed valve 7. The dead end space 19 is positioned at a farmost position from the electromagnetic valve 1 to suppress a temperaturerise due to the exhaust gas in a space around the electromagnetic valve1.

The barrier 51 includes a bent portion 55 for preventing foreignparticles once entered into the dead end space 19 from bouncing outagain into the air passage 16. The bent portion 55 is bent downwardly sothat the opening 54 becomes narrower than an inside space of the deadend space 19. A curved surface 57 is formed above the dead end space 19.The curved surface 57 facilitates a smooth flow of the secondary airflowing out through the plural openings 15 of the metal plate 41.

Now, operation of the airflow control valve described above will beexplained. A three-way catalyzer for converting CO, HC and NOx containedin the exhaust gas into harmless components is installed in an exhaustpipe of an automobile. To realize a good conversion reaction in thethree-way catalyzer, it is required to keep air-fuel mixture supplied toan internal combustion engine at a stoichiometric ratio (15:1) and toraise the exhaust gas temperature above a certain level, e.g., 350° C.When the exhaust gas temperature is low, e.g., when the engine is beingstarted, secondary air is supplied from an air pump to the three-waycatalyzer to raise its temperature. By supplying air to the three-waycatalyzer, the catalyzer is activated by heat generated by burninghydrocarbons contained in the exhaust gas.

The secondary air is supplied from the air pump to the three-waycatalyzer through the airflow control valve. When the secondary air isrequired, the valve 2 is opened under the control of the ECU, and thesecondary air is sent through the upstream passage 11, 12, the opening13, the passage 14, the opening 15 and the downstream passage 16, 17, asshown with white arrows in FIG. 2. In this case, the one-way valve 6 isopened by the pressure of the secondary air. The secondary air smoothlyflows along the curved surface 57 toward the outlet port 18. Thus, thethree-way catalyzer is activated to convert harmful components in theexhaust gas into harmless components.

When the valve 2 is closed, the blown back exhaust gas enters into theair passage 16, 17. Particles contained in the exhaust gas form depositson and around the reed valve 7 of the one-way valve 6. When a certainamount of the deposits is accumulated on and around the reed valve 7,the reed valve 7 becomes unable to close. If the one-way valve 6 doesnot function as a one-way valve, the exhaust gas entered the air passage16 further proceeds to the air passage 14 through the opening 15 of theone-way valve 6. If this happens, it is highly possible that depositsare formed on and around the valve 2, making the valve 2 unable to workproperly. If the valve 2 does not work properly, a sufficient amount ofthe secondary air will not be supplied to the three-way catalyzer.

In order to avoid the trouble mentioned above, the dead end space 19 isformed in the outlet casing 9 according to the present invention. Asshown in FIG. 2 with dotted arrows, the exhaust gas blown back from theexhaust pipe enters into the air passage 16, 17 along a bottom wall 56and proceeds to the dead end space 19 through the opening 54. Theexhaust gas entered into the dead end space 19 hits the wall of the deadend space 19 and stagnates therein. Therefore, an amount of the exhaustgas directly hitting the one-way valve 6 is reduced. Accordingly,formation of the deposits on and around the reed valve 7 is suppressed.Further, the opening 54 of the dead end space 19 is made narrower thanthe inside space, and the bent portion 55 is formed at the opening 54.Therefore, the exhaust gas once entered into the dead end spacecirculates therein, keeping the foreign particles contained in theexhaust gas in the dead end space.

Thus, formation of the deposits on and around the one-way valve 6 andthe valve 2 is suppressed, thereby securing proper operation of theairflow control valve. Further, since the dead end space 19 is formed atthe position far from the valve 2, a temperature rise in theelectromagnetic valve 1 due to the exhaust gas is suppressed. Since thecurved surface 57 is formed above the dead end space 19, the secondaryair smoothly flows through the air passage 16, 17 when the valve 2 isopened. The foreign particles accumulated in the dead end space 19 whenthe valve 2 is closed are sucked back again into the exhaust pipetogether with the secondary air when the valve 2 is opened. Accordingly,it is not necessary to provide a dead end space 19 with a large size orto provide additional means for scavenging the dead end space 19.

A second embodiment of the present invention will be described withreference to FIG. 3. In this embodiment, a shape of the barrier 51 inthe first embodiment is modified to a barrier 51 a shown in FIG. 3. Thebarrier 51 a includes a passage surface 52 a standing up from the bottomwall 56 at a right angle. A stagnating space 59 is formed between theair passage 17 and the passage surface 52 a.

The exhaust gas blown back from the exhaust pipe and entering into theoutlet casing 9 from the outlet port 18 hits the passage surface 52 a.An amount of exhaust gas directly hitting the one-way valve 6 isreduced, and the exhaust gas stagnates in the stagnating space 59.Foreign particles included in the exhaust gas form deposits in thestagnating space 59 or accumulates therein. Thus, an amount of depositsformed on and around the reed valve 7 is reduced. In this manner, thebarrier 51 a in the second embodiment functions similarly to the barrier51 in the first embodiment.

A third embodiment of the present invention is shown in FIG. 4. In thisembodiment, a barrier 51 b is further modified from the barrier 51 a ofthe second embodiment. The barrier 51 b includes a passage surface 52 bstanding up from the bottom wall 56 forming an acute angle. A stagnatingspace 59 b is formed between the air passage 17 and the passage surface52 b. The amount of exhaust gas directly hitting the one-way valve 6 isreduced in the same manner as in the second embodiment. Further, in thisthird embodiment, the foreign particles in the exhaust gas once kept inthe stagnating space 59 b are prevented from bouncing out of thestagnating space 59 b by the passage surface 52 b forming an acute anglebetween itself and the bottom wall 56.

A fourth embodiment of the present invention will be described withreference to FIGS. 5-9. In this embodiment, as shown in FIGS. 5 and 6,an interfering wall 61 standing up from the bottom wall 56 at a rightangle is formed in the inner space of the outlet casing 9. Theinterfering wall 61 has a wall surface 62 directly facing the outletport 18, and a stagnating space 64 is formed between the air passage 17and the wall surface 62. As shown in FIG. 6 the interfering wall 61further includes a pair of bent portions 63 bent toward the outlet port18. Further, passage surfaces 66 having an inclination as shown in FIG.6 are formed on an inner wall of the outlet casing 9 for smoothlyguiding the secondary airflow sent through the valve 2 to the outlet 18.An air passage 67 converging to the outlet port 18 is formed by thepassage surfaces 66. Holes 43 (shown in FIG. 6) are holes for connectingthe outlet casing 9 to the valve housing 3 with screws or the like.

As shown in FIGS. 7 and 8A (an exhaust gas flow is shown with dottedarrows and a secondary airflow is shown with white arrows), the exhaustgas entering into the air passage 17 from the outlet port 18 hits theinterfering wall 61 and stagnates in the stagnating space 64. A certainamount of foreign particles included in the exhaust gas is kept in thestagnating space 64, and an amount of exhaust gas hitting the one-wayvalve 6 is reduced. The foreign particles once kept in the stagnatingspace 64 are prevented from bouncing out of the stagnating space 64toward the one-way valve 6 by the pair of bent portions 63. In thismanner, an amount of deposits formed on and around the reed valve 7 isreduced.

The interfering wall 61 could be an obstacle to the secondary airflowsupplied from the air pump through the valve 2. To avoid the interferingwall 61 from becoming an obstacle to the secondary airflow, as shown inFIG. 8A, the inclined passage surfaces 66 are formed on the inner wallof the outlet casing 9, and inclined surfaces 65 along the secondaryairflow are formed on the bent portions 63. A smooth air passage 67 forthe secondary airflow is formed by the inclined passage surfaces 65, 66.Therefore, the secondary air smoothly flows through the air passage 67without generating a high amount of pressure loss.

The outlet casing 9 in the fourth embodiment may be further modified toa form shown in FIGS. 8B and 9. In this modified form, a barrier 71 isformed in the outlet casing 9. The barrier 71 includes a passage surface72 directly facing the outlet 18 so that the exhaust gas entering intothe outlet casing 9 hits the passage surface 72. The passage surface 72stands up from the bottom wall 56 at a right angle, and a stagnatingspace 74 is formed between the barrier 71 and the outlet port 18. Bentportions 73 for preventing the foreign particles once trapped in thestagnating space 74 from easily bouncing out of the stagnating space 74are formed on the passage surface 72. Further, inclined passage surfaces75 for smoothly guiding the airflow 76 of the secondary air toward theoutlet port 18 are formed.

The exhaust gas entering into the air passage 17 from the outlet port 18hits the passage wall 72 and stagnates in the stagnating space 74.Foreign particles in the exhaust gas are accumulated or deposited in thestagnating space 74. An amount of the exhaust gas directly hitting theone-way valve 6 is reduced, and an amount of foreign particles depositedon and around the reed valve 7 is reduced. The secondary air suppliedfrom the air pump through the valve 2 is smoothly led to the outlet port18 along the inclined passage walls 75.

The present invention is not limited to the embodiments described above,but it may be variously modified. The barrier and/or the stagnatingspace for the exhaust gas according to the present invention may beapplied to various valves such as a swirl control valve, an intake-aircontrol valve in a swirl control valve, a tumble control valve, anintake-air control valve in a tumble control valve, or a throttle valvefor controlling amount of intake-air. The present invention may beapplied also to an exhaust gas re-circulating valve for supplying acertain amount of exhaust gas into an air-intake pipe of an internalcombustion engine.

While the present invention has been shown and described with referenceto the foregoing preferred embodiments, it will be apparent to thoseskilled in the art that changes in form and detail may be made thereinwithout departing from the scope of the invention as defined in theappended claims.

1. An airflow control valve for use in an internal combustion engine,the airflow control valve comprising: a housing forming an air passagetherein; a valve disposed in the air passage for opening or closing theair passage, the air passage being separated by the valve into anupstream passage having an inlet port and a downstream passage having anoutlet port from which air is blown out, the outlet port being open to asource of exhaust gas exhausted from the internal combustion engine; anda barrier disposed in the down stream passage to face the outlet portfor reducing an amount of the exhaust gas directly hitting the valvewhen the exhaust gas enters the downstream passage from the outlet port.2. The airflow control valve as in claim 1, wherein: the barrierincludes a passage surface facing the outlet port; and a stagnatingspace for stagnating the exhaust gas flow is formed in the vicinity ofthe passage surface.
 3. An airflow control valve for use in an internalcombustion engine, the airflow control valve comprising: a housingforming an air passage therein; a valve disposed in the air passage foropening or closing the air passage, the air passage being separated bythe valve into an upstream passage having an inlet port and a downstreampassage having an outlet port from which air is blown out, the outletport being open to a source of exhaust gas exhausted from the internalcombustion engine; and a dead end space disposed in the downstreampassage to face the outlet port for stagnating the exhaust gas enteringinto the downstream passage from the outlet port, the dead end spacehaving an opening from which the exhaust gas enters.
 4. The airflowcontrol valve as in claim 3, wherein: the dead end space includes apassage surface facing the outlet port, and the opening of the dead endspace open to the passage surface.
 5. The airflow control valve as inclaim 3, wherein: the opening of the dead end space is smaller than aninside of the dead end space.
 6. The airflow control valve as in claim3, wherein: a bent portion for preventing foreign particles, containedin the exhaust gas, once entered into the dead end space from bouncingout of the dead end space is formed at the opening of the dead endspace.
 7. The airflow control valve as in claim 6, wherein: the bentportion is formed at a portion of the opening close to the valve.
 8. Anairflow control valve for use in an internal combustion engine, theairflow control valve comprising: a housing forming an air passagetherein; a valve disposed in the air passage for opening or closing theair passage, the air passage being separated by the valve into anupstream passage having an inlet port and a downstream passage having anoutlet port from which air is blown out, the outlet port being open to asource of exhaust gas exhausted from the internal combustion engine; andan interfering wall disposed in the downstream passage for interferingwith a flow of the exhaust gas entering into the downstream passage fromthe outlet port.
 9. The airflow control valve as in claim 8, wherein:the interfering wall includes a wall surface directly facing the outletport; and a stagnating space for stagnating the exhaust gas therein isformed between the wall surface and the outlet port.
 10. The airflowcontrol valve as in claim 9, wherein: the downstream passage includespassage surfaces inclined along a flow direction of the air to be blownout from the outlet port so that the air smoothly flows through thedownstream passage.
 11. The airflow control valve as in claim 1,wherein: the upstream passage is a passage for introducing compressedsecondary air to be supplied to an exhaust pipe of the internalcombustion engine; the downstream passage is a passage for supplying theair to the exhaust pipe of internal combustion engine; and the valve isa valve for controlling an amount of the secondary air to be supplied tothe exhaust pipe of the engine by opening or closing the air passage.12. The airflow control valve as in claim 11, wherein: a one-way valvefor preventing the exhaust gas from entering into the upstream passageis provided in the downstream passage.
 13. The airflow control valve asin claim 12, wherein: the one-way valve includes a metal plate havingair passages through which the secondary air flows, a reed valve foropening or closing the air passages, and a reed valve stopper forlimiting an opening degree of the reed valve; and the one-way valve ispositioned in the vicinity of the valve.
 14. The airflow control valveas in claim 1, wherein: the air passage is a passage for connecting anexhaust pipe to an intake pipe of the internal combustion engine forre-circulating part of the exhaust gas to the engine for decreasing acombustion temperature in the engine, and an amount of the exhaust gasto be re-circulated is controlled by the valve.